1. Field of the Invention
This invention relates to measuring devices utilizing a variable color display.
2. Description of the Prior Art
Commercially available measuring instruments with monochromatic digital readout are capable of performing measurements and displaying results at a relatively fast rate. However, to determine a significance of each measured value, an operator must rapidly read displayed values and perform mental comparisons with predetermined limits. The task is much more complicated when the limits are variable.
A system for measuring radioactivity is described in U.S. Pat. No. 2,643,344, issued on Jun. 23, 1953 to Ian H. McLaren et al. Another systems for measuring radioactivity are described in U.S. Pat. No. 2,648,015 issued on Aug. 4, 1953 to Alexander Greenfield et al., and in U.S. Pat. No. 2,682,000 issued on Jun. 22, 1954 to Joseph F. Clayton et al. Since these three patents are very similar, they are equally authoritative. The system for measuring radioactivity, disclosed in the three patents, includes an analog pointer indicator having three scales, with three associated colored light bulbs, for indicating which scale is applicable for the reading of the measured value. A mechanism for automatic range selection is provided, which is controlled by two solenoids, and which also controls the three associated colored light bulbs. In response to the range selection, one of the light bulbs illuminates the indicator face with a distinctive color to indicate which measurement scale is applicable. After each measurement, the operator must evaluate each measured value to determine its significance, mentally or otherwise.
A digital meter is disclosed in U.S. Pat. No. 2,889,518, issued on Jun. 2, 1959 to Harold R. Hudson et al. The digital meter includes a motor, a wheel counter rotatable by the motor, a potentiometer rotatable by the motor, and a mechanical sampler (vibrator). An unknown voltage is compared, by the sampler, with an instant reference voltage that appears on the wiper of the potentiometer. The motor keeps rotating the potentiometer until the unknown voltage is equal to the reference voltage. The rotation of the motor is then automatically stopped, which also stops the wheel counter, whose position numerically indicates the value of the measured voltage. The decimal point monochromatic lamps are placed between the wheels of the counter. One of the decimal point lamps is illuminated, by manually operated range switch, to indicate by its position the selected measurement range.
The prior art does not contemplate a digital voltmeter capable of automatically evaluating the measured value. The prior art does not contemplate a digital voltmeter capable of automatically indicating a significance of the exhibited measured value, by color. The prior art does not contemplate an analog comparator for automatically comparing the value of an analog measured signal with an analog limit, to determine their relation.